Members of Japan's Self-Defence Forces' airborne troops stand at attention during the annual SDF troop review ceremony at Asaka Base in Asaka

Japanese Prime Minister Shinzo Abe is now following through on actions laid out in his recent bold speech calling for Japan to defend allies who might be under attack.

But wait, you may ask, hasn’t the United States had a mutual security treaty with Japan for more than half a century?

Well, not quite. Yes, Washington has had a mutual defense-security treaty with Tokyo since 1951. But Japan is not committed to defending the United States or any of its armed forces. In fact, Japanese forces are prohibited from helping Washington in time of war — even if the war is in defense of Japan.

This goes back to the postwar U.S. Occupation of Japan and the creation of the Japanese constitution. Determined that Tokyo would never again pose a threat to its Asian neighbors or the United States, Occupation leader General Douglas MacArthur and his staff were sympathetic to Japanese pacifists’ proposal to include a no-war making article in the constitution, then being written with oversight by the Occupation authorities. This worked with the policies of then-Prime Minister Shigeru Yoshida, who wanted to focus on rebuilding the Japanese economy — without the distraction of creating a major defense force.

Japan's PM Abe speaks during a news conference at his official residence in TokyoSo Japan’s constitution prohibits engagement in war. Despite using the term “mutual” to describe the U.S.-Japan agreement, there has never been anything mutual about it. It has always been a unilateral U.S. guarantee of Japan’s defense.